[GreenKeys] 6 Unit TTS Coding...

[Don Robert House]

Thanks much Rice,
This is a good explanation. I sure do appreciate your time and efforts.
Best,
Don
Duncan Here is (Hopefully) your answers Ref: Navships manual Page C-6  
Para 4.0 SIX Unit Code
The characteristics of the 6-unit code are similar to those of the 5- 
unit code, except that the combination of signals for each character  
consists of six elements of the six elements of equal duration for a  
total of (2 to the 6th power) or 64 combinations.
Thus it is possible to fulfill all the functions performed by the 5- 
unit code without the case shift signals.
This offers advantages for traffic involving a mixture of letters and  
figures, since the elimination of the operations in involved in the  
insertion of shift-signals saves time in the transmission of messages.
An example of this type of traffic is stock exchange, which employ 6- 
unit teletypewriters.
Now for the modulation rates between these two
                             WPM	CPS  BR   BPS  UPC	WBPC	SP CBS	OPM	NB/W
5 LEVEL CODE	61.3	6.13	45.5	42.91	7.42	21.97	31.2	163	367.8	136.5
6 LEVEL CODE 61.3	6.13	49.04	49.04	8.0	20.4	20.4	163.2	367.8	147
(Note: the big difference in the stop bit timing!) In short the 6 unit  
code eliminates the need to go upper case and lower case between LTRS  
and FIGS which provides a faster character/word through put vice time.
(Note the higher BAUD rate at 6 level vice 5 level) I remember working  
on Don's M20 and had my test set set for 5 level code and I got good  
copy once in a while.
The above explains why. As for the gear change needed per Dons remark,  
both 5 and 6 levels operate at 368 operations per minute (main shaft  
speed) so why Teletype Corp. made the gear change is beyond me, but  
they did a lot of funny things or I'm missing something!
Rice